Phantom carrier circuits



April 27 1926.

H. A. AFFEL PHANTOM CARRIER CIRCUITS Filed August 1l, 1925 Sww n, www wam? A NQAIL.

PatentedV Apr. 27, 1926.

UNITED STATES HERMAN A. AFEEL, or MAPLEWOOD, NEW JnRsnY, Assrenon To AMERICAN TELE PATENT OFFICE.,

PHONE ANDTELEGRAH COMPANY, A OORPORATION OF NEW YORK.

i rHANToM CARRIER cincorrs.

Application filed August il, 1925. `Serial No. 119,60*?.

4To all ltti/"wm t muy concern.' c

Be it known that l, HERMAN A. AFFEL, a citizen ot' the UnitedStates, residing at ldaplewood.l in the count37 of Essex and State of New Jersey, have invented certain improvements in Phantom Carrier Circuits,

et which the 'following is a specification.

rl.1 his invention relates to transmission circuits and more particularly to arrangements tor employing carrier transmission upon phantom conductive systems. p

It hasV heretofore beenthe practice in ordinary telephone transmission tti-phantom the telephone circuitsA so that each pair of conductorsnot only acts as a series concluetive: system or aside circuit, but also lacts as one side ot a phantom circuit, the two conductoisV in. parallel constituting one conductor ot the phantom. path while the two conductors ot a similar side circuit .operate in parallela's the return path for the phantom. circuit. lt has not, however., been ther practice to utilize the phantom 'circuits thus formed forcarrier transmission because the requirements with respectto unbalance and crosstall: at carrier frequencies have been too great. The ycarrier 'frequency unbalance and c-rosstalk of the phantom are gradually being` reduced, however, and there is now presented the problem of associating iilterswith each other so as to properly separate the. side voice circuits and side carrier circuits. from each other andat the same and from the side circuit channels.

' It is one of the objects of the present in-A vention to provide ay suitable arrangement ol' iilters for ettectino the necessar i se iai-ation between the various types of circuits without introducing undesirable transmission losses and without producing any undesirable etfects upon the ilters due vto the presence in the same network of other filters'.

These objects as well as other objects of the invention may be attained by means of the arrangementsset. forth in the following description and illustrated in the accom,- panyi'ng drawing, the ligure of which shows a circuit diagram embodying` the invention in its preferred form. p Referring` to the drawing, H'FL and HFL represent two telephone lines, each comprisi ingI a pair of conductors which may ybe phantomed in a well known manner so that" n telegraph transmission.

veach pair ot conductors acting in parallel opand il are led to form the phantom termi-A l kr Composite sets CX and Da are included in the linesv EFL and nals of the system.

HFL by means ot' which each ot' the four conductors may be employed for Morse The composite sets are mereljrshown schematically in the drawing,v theseV sets being of a type welllnoi'rn intheart soV that detailed illustration is un necessary.v

lnbrder that the line HFL may be ein-` provved' tor carrier transimssion,` a branch CLS is `provided which leads to carrier equipment oi' anT type well known in the art, and inthls lnanelji a high oas-s iilter HFS is included. This'l'iigh pass iiter is oi the broad bandty'pe which Aitreely .transmits a band of v frequencies within certain limitslwhile sharpl;7 attenuatine and suppressing the trelquencics lyingV`V` without the ,limits-of the baud.'v The hlte'r isfso designed as to pass Vthe various carriercfrequencies Aemployed in the system together with their associated side bands', but it 'will not permit ordinaryvoice currents transmitted over the line HFL to pass into the circuit CLS. The ordinaiw7 voice currents transmitted over tlieconductor EFL must be separated from the carrier frequencies and transmitted through the transformer l0 to-thev'oice side circuit rchany nel Vla. y ln order to accomplish this result` a.

low pass filter LFg isconnected in the branch` ofthe, line circuit HEL leading; to the voice side'circu'itjVLs. Theiilter LFS is ot the broadliand tvpc and' iiieeljv transmits all frequencies y'lying within the voice range while suppressing; all frequencies above the through the high pass filter HFQ to the side carrier circuit CLS and the other leading through the low pass filter LFS to the voice side circuit VLS;

The `arrangement so tar described is that lUO ordinarily ei'nployed for superposin'g a plun n ralityof carrier channels onanordinary voice'channel. It is possible `to phantom a pair of circuits of this type for ordinary voice transmission by means of the phantom coils l() and 10 with their phantom conductors 1l and l1. This follows at once from the fact that the unbalance between the phantom circuit and the side circuits at voice frequencies is no greater with the arrangement above described than in the case of circuits which are not arranged for multiplex carrier transmission, and the voice currents transmit-ted ever the phantom, in so far as any imbalance occurs between the two conductors of the side circuit, are prevented from entering the carrier circuit, such as the circuit CLS, by the high pass filter. The effect upon the phantom of the filter LFS in the two conductors of the side circuit is to introduce impedance due to the series coils of the filter but this impedance is not serious at the ordinary voice frequencies. If, however, we attempt to transmit carrier frequencies over the phantom, the inductance of the series elements of the filter LFS or LFS is relatively much greater, so that not Vonly must this problem be overcome but the problem of selection between the carrier phantom and the voice phantom must also be overcome.

in accordance with the present invention the latter difficulty is met by providing the phantom terminal comprising the conductors 1 1 and l1 with two parallel branches, one branch Clt, leading to kthe phantom carrier equipment and the oth-er branch VLp leading to the voice equipment. A high pass filter HFD of ordinary construction is included in the phantom carrier branch CLp and a low pass filter LFp of ordinary construction is included in the voice phantom circuit VLD.

The effect of the two filters LFI, and HFI, upon the part of the circuit including the phantom leads 1l and 11 is to eHect the same kind of separation between the voice channel and the carrier channels as is effected between the corresponding side channels by means of lter combinations such as LFE and HFS. There still remains, however, the problem of preventing the filter LFE from cutting down the transmission of the carrier frequencies which may be transmitted over the phantom through the high pass filter HF? The shunt elements of the filter LFB are condensers and do not cut down the transmission over the phantom because they are bridged across points of substantially equal potential (so far as the phantom is concerned) between the two conductors of the side circuit. The series inductance coils, however, are directly included in the phantom circuit and must be taken into account. In order to eliminate the effects of these coils, it is proposed in accordance with the present invention to mount the windings included in each line conductor upon a common core and to so wind the coils about the core that the inductances in the two line conductors neutralize cach other. Vhen so wound, it will be clear that for currents flowing serially over the two conductors of the side circuit the coils of the filter will be series-aiding and will introduce the necessary induetance into the several sections of the filter so that it may perform its ordinary function. Then current is flowing over the two conductors in parallel, however, the windings being mutually opposed, no inductance is introduced in the circuit and the filter, such as LFS, is without effect.

lt will, of course, be clear that for carrier currents transmitted over the phantom conductor il, the filter HFS which is bridged across the side circuit, will be ineffective since said filter is bridged across equal potential points of the side circuit with respect to the phantom carrier current. Consequently, if the two side conductors of the side circuit are properly balanced with respect to the phantom, there will be no interference between the phantom carrier channel and the side circuit carrier channel.

It will be obvious that the general principles herein disclosed may be embodied in many other organizations widely differentfrom those illustrated wit-hout departing from the spirit and scope of the invention as defined in the appended claims.

TWhat is claimed is:

l. ln a transmission system, a pair of side circuits each adapted for the transmission of voice frequency currents and also for the transmission of carrier currents, a pair of terminal branches for each side circuit, a low pass filter in one branch of each pair to permit the transmission of voice currents over said branch while suppressing the transmission of carrier frequency currents transmitted over the conductors of the side circuits in series, a high pass filter in the other branch of each pair to readily transmit carrier currents from terminal carrier equipment to and from the side circuit while preventing voice frequency currents from entering said branch, means to establish a phantom connection adjacent one end of the low pass filter associated with each side circuit to form a phantom circuit, branches for said phantom circuit, a low pass filter in one of said branches to permit voice frequency currents to be transmitted over the phantom to and from said branch while suppressing carrier frequency currents from said branch, and a high pass filter in the other branch to permit the transmission of carrier frequency currents over the phantom to and from said branch while suppressing the transmission of voice frequency currents.

2. In a transmission system, a pair of transmission lines adapted to transmit either ordinary voice frequency currents or carrier frequency currents, a pair of branches for each line, one branch extending to a Voice frequency terminal, the other branch extending to carrier equipment, a louT pass filter-in said first mentioned branch and a high pass filter in said second mentioned branch of each line, means to connect a phantom conductor to the first mentioned branch of each line so that currents transmitted over the phantom conductor will be transmitted over the two sides of the line in parallel, the phantom conductors of the two lines forming a phantom circuit over which Voice frequency currents and carrier frequency currents may be tansmitted, a pair of branches for the phantom circuit, one of said branches extending to a Voice frequency terminal and the other branch extending to carrier equipment, a low pass filter in said first mentioned branch, and a high pass ilter in said secondmentioned branch.

3. In' a transmission system,J a pair of transmission lines adapted to transmit either Voice frequency currents or carrier frequency currents, a pair of branches for each line, one branch extending` toa Voice frequency terminal and the other branch extending to carrier equipment, a 10W pass ilter in said first mentioned branch `of each 1 line and a high pass filter in said second mentioned branch of each line, said loW pass filter comprising a plurality of sections each of which consists of a series inductance and a shunt impedance element, the series in- Vductance of each element being divided so that part of the inductance Will be in one l conductor of the circuit and the other part of the inductancel Will be in the other con` f ductor of the circuit, said inductances being so Wound and related With respect to each other that the coils in the two conductors will be mutually aiding With respect to y currents transmitted over the conductors in series but Will be mutually opposing with respect to currents transmitted over the'conduc-tors in parallel, a phantomcoil :inter-`r posed between said low pass lilter and said voice frequency terminals for each line, al

circuit, one of said branches extending` to a voice frequency terminal, the other branch extending to carrier equipment, a 10W pass filter in said .first mentioned branch of the phantom circuit, and a high pass filter in said second mentioned branch ofthe phantom circuit. c n

In testimony whereof, I have signed my name to this specification this 10th day of August, 1925. y 

